This invention relates generally to the field of improving the pigmentation and stability of anthocyanin-containing foods and beverages using compounds easily obtainable from naturally-occurring plant materials.
An attractive and stable color is important to the marketability of foods and beverages. Synthetic coloring agents have commonly been used in the food and beverage industry. The safety of synthetic coloring agents, however, has been questioned. For example, the Food and Drug Administration has delisted red dyes No. 2 and No. 4. In general, consumer confidence in synthetic food materials has waned. Thus, the need exists for naturally-occurring pigments.
Anthocyanins are found in many naturally occurring foods and can serve as pigments to impart a wide range of colors. Anthocyanin pigments are biodegradable and water soluble; they are not suspected toxins or carcinogens. In fact, Miniati and Coli have reported that ingested anthocyanins can lower cholesterol, inhibit platelet aggregation, and exhibit anti-thrombotic and antioxidant properties. (Miniati, E. and Coli, R., "Anthocyanins: Not only Color for Foods," The First International Symposium on Natural Colorants, Francis, Dr. F. J., Ed. (1993) available through the Herald Organization, Hamden, Conn.)
Despite those beneficial attributes, anthocyanin pigments have not been widely used as food additives for several reasons. Anthocyanins are difficult to purify which makes obtaining commercially useful quantities difficult. (Mazza, G. and Brouillard, R. "Recent Developments in the Stabilization of Anthocyanins in Food Products," Food Chemistrv, Vol. XXV, pp. 207-225 (1987)). The color of anthocyanin preparations has been reported to be two orders of magnitude weaker than that of synthetic compounds. (Ibid.) Anthocyanins in aqueous solution are degraded by heat, light, enzymes, nucleophiles, oxygen and ascorbic acid.
Acylated anthocyanins have been discovered that retain color over a broader pH range. See, e.g, U.S. Pat. No. 4,172,902. However, source materials for acylated anthocyanins are limited as are the colors which acylated anthocyanins impart. Purified acylated anthocyanins have not been approved as food additives. Thus, it is problematic to improve the color of food products by simple addition of acylated anthocyanins at the present time.
It is highly desirable to improve the performance of anthocyanin pigments as additives for food products. As used herein, the term "food product" includes both solid edible substances and liquid beverages. The term food "additive" refers to a material that is applied to or inserted into a food product. It is particularly useful to find pigment-improving agents that protect, i.e., "stabilize," anthocyanins from color loss due to pH, heat, and/or light. Preferably, the pigment-improving agents are, like the anthocyanins, naturally occurring, biodegradable and water soluble and have no known toxic or carcinogenic effects.
The use of certain compounds, particularly flavonols, to improve the stability of anthocyanin pigments in foods has previously been suggested. See, U.S. Pat. No. 4,285,982, which also recognizes that the use of many naturally-occurring flavonols for this purpose is not "attractive," because of their limited availability and poor water solubility. Indeed, U.S. Pat. No. 4,285,982 teaches the use of certain compounds which are derived by synthetic means. These synthethic materials must be subjected to expensive and time-consuming tests to demonstrate compliance with rigorous regulatory requirements before commercial application. Even then they will always have diminished marketability due to their stigma as non-natural food additives.
It has long been known that flavonoids are often associated with anthocyanins in plants. Certain flavonoids have been shown in vitro to cause both a bathochromic and hyperchromic shift in the absorption spectrum of anthocyanins. The "bathochromic shift" refers to an increase in the wavelength at which the absorbance is greatest, the .lambda..sub.max. The "hyperchromic shift" refers to an increase in absorbance at .lambda..sub.max. The shift in .lambda..sub.max and increase in absorbance is called "copigmentation." Copigmentation results in a color shift toward a longer wavelength and a more intense color than that seen with the anthocyanin alone. Copigmentation of anthocyanins with plant flavonoids is believed responsible for the wide range of color shades found in flowers.
Asen et al. have identified several naturally-occurring copigments, including flavonoids. (S. Asen, R. N. Stewart and K. H. Norris; "Copigmentation of Anthocyanins in Plant Tissues and its Effect on Color," Phytochemistry, 11, 1139 (1972)). Asen et al. measured and reported the copigmentation potency of many of these compounds, as shown by their hyperchromic and bathochromic shifts. The most potent of these copigments have limited availability and water solubility. They are not good candidates as pigment-improving agents for anthocyanin food additives.
Asen et al., were interested in identifying and modifying the color of flowers. In that endeavor they isolated two flavonoid glucuronides from two different flower types, "Blueboy" cornflowers and "Better Times" roses, respectively. Asen and Horowitz attributed the color of Blueboy cornflowers to copigmentation of anthocyanins with apigenin 4'-O-beta-D-glucoside 7-O-beta-D-glucuronide. (Asen, S. and Horowitz, R. M., Phytochemistry, Vol. 13, pp. 1219-1223 (1974)). Asen et al. extracted several flavonol glucosides and quercetin 3-glucuronide from Better Times roses and identified these flavonols as anthocyanin copigments responsible for the color of that rose. (Asen et al., J. Amer. Soc. Hort. Sci., 96 (6): 770-773 (1971)).
Neither Asen reference, however, recognizes the effect of these glucuronides on anthocyanin stability, their potency, or their availability. Indeed, the art does not show or suggest that those glucuronides or any other derivatives of glycuronic acid would have commercial value as pigment-improving agents for anthocyanin-containing products, especially foods. As used herein "pigment-improving agent" refers to a compound which is both a copigment and stabilizer of anthocyanin-based color. References to "improving" pigmentation mean to concomitant copigmentation and stabilization of anthocyanin-based colors.